Question

Sino-atrial node $(SAN)$ is called the pacemaker. $SAN$ generates the maximum number of action potentials and is responsible for initiating and maintaining the rhythmic contractions of the heart

• A. If both assertion and reason are true and reason is the correct explanation of assertion
• B. If both assertion and reason are true but reason is not the correct explanation of assertion
• C. If assertion is true but reason is false
• D. If both assertion and reason are false

Answer 1

Answer: (A)

If both assertion and reason are true and reason is the correct explanation of assertion

Answer 2

In the myogenic heart, contraction is initiated by specialised muscles. The $SAN$ can generate the maximum number of action potentials, i.e., $70-75\, min^{-1}$, and is responsible for initiating and maintaining the rhythmic contractile activity of the heart. Therefore, it is called the pacemaker. The $SAN$ controls the beat of the heart because its rate of rhythmical discharge is faster than that of any other part of the heart. Therefore, the $SAN$ is virtually always the pacemaker of the normal heart.